This invention relates to a method of controlling plate flatness of a rolled material.
Heretofore, in the plate rolling field, there has been proposed a control to use a plurality of manipulated variables at the same time, thus to utilize the characteristics of respective manipulated variables at their maximum in order to cope with a control for various patterns damaging the plate flatness such as edge wave, center buckle, quarter buckle or complex buckle. As a representative example thereof, there has been proposed, as shown in the Japanese Patent Application No. 153165/80, a plate flatness feedback control in which the working roll bending and the intermediate roll bending are used at the same time, thus taking into consideration the degree of influence or effect on the plate flatness of the respective roll bending actions.
However, as a matter of course, the operating ranges of respective manipulated variables of the working roll bending or the intermediate roll bending, etc. have upper and lower limits. Thus, only operation in a limited range is permitted. Further, in the case where the operating speed is extremely slow, as for roll shift, as compared to that for roll bending, correction quantities of the variables are also limited. Accordingly, since consideration is not sufficiently taken for the above limits in the conventional method, a control, such that the characteristics of respective manipulated variables are sufficiently exhibited, does not result.
In addition, as disclosed in PCT/JP81/00285, there is proposed a method of approximating a buckle rate signal divided in a width direction by a higher-order polynominal with respect to the width direction, developing the polynominal into an orthogonal function series, thus to determine manipulated variables by utilizing the fact that the influences of coefficients of respective function series and manipulated variables of the actuator subject to control have a correspondence relationship therebetween sufficient to control. However, satisfactory control cannot be obtained even by this method.